Fashion vs. Function in Cultural Evolution: The Case of Dog Breed Popularity

The dynamics of dog breeds popularity have been recently used to test various assumptions of models of cultural evolution. Bentley et al. (Random drift and large shifts in popularity of dog breeds) found that the cumulative distribution of breeds popularity (i.e. how many dogs of each breed have been registered overall – in a period covering years from 1946 to 2001) roughly follows a power-law, meaning that very few breeds totalised the great majority of the registrations, and the great majority of breeds totalised proportionally very few registrations. Power-laws are ubiquitous in natural (the distribution of earthquakes magnitude) and socio-cultural (the distribution of wealth, the frequency of words in books, etc.) phenomena, and Bentley et al. showed that, for socio-cultural phenomena, these distributions can be produced by a simple “neutral” model of cultural evolution, which assumes that individuals just copy randomly cultural traits (dogs, in the specific case) from each other.

Subsequently, together with Stefano Ghirlanda and Magnus Enquist (The logic of fashion cycles), we used the same data focusing on another feature of dog breeds popularity, i.e. the fact that there is a correlation between the speed of increase in popularity of a breed and the speed of decrease: dogs that become quickly popular tend also to become quickly unpopular, and vice-versa (see the Rottweiler example below, many others here). To explain this feature – also found for baby names – we proposed a slightly more complicated model of cultural evolution, in which individuals may copy from each other not only cultural traits (the dogs) but also preferences for cultural traits (“I love Dalmatians!”). One of the property of this model is that individuals with low preferences for popular cultural traits tend to be better “influencers” (this is quite counterintuitive and, I think,  interesting – you can have a look here), so that, in the model, when a cultural trait becomes quickly popular, preferences for this cultural traits also become quickly negative, generating the correlation we found in the data.

dogs

Both models, however, assume that what drives the popularity of dog breeds is social influence (“fashion”). This is paradoxical: given that people presumably ponder their choice when deciding to have a pet, one would expect that features of breeds (“function”) would be more important in this decision. We just published a paper in which we take on this question. We used data on longevity, health, and behavioural characteristics of breeds (such as aggressivity, trainability, attachment, etc.) and correlated them with various popularity measures (speed of increase and decrease, total popularity, and volatility) to see which features were influencing more the popularity. The answer? None!

A part of taking a clear side in the debate whether to publish or not negative results, I think that there are some interesting conclusions from our analysis. Either social influence can indeed be, at least in some domains, a “blind” force that almost autonomously generates cultural dynamics, or – as I now prefer to think – it is tricky to recognise, from population level data, biases acting at individual level. This seems to me a quite interesting problem for people studying cultural evolution.

References

Acerbi A, Ghirlanda S, Enquist M (2012) The Logic of Fashion cycles. PLoS ONE  7(3): e32541

Berger J, Le Mens G (2009) How adoption speed affects the abandonment of cultural tastes, PNAS 106(20): 8146–8150

Herzog H, Bentley RA, Hahn MA (2004) Random drift and large shifts in popularity of dog breeds. Proceedings of the Royal Society B 271: S353–S356

Ghirlanda S, Acerbi A, Herzog H, Serpell JA (2013) Fashion vs. Function in Cultural Evolution: The Case of Dog Breed Popularity. PLoS ONE 8(9): e74770.

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